The present invention relates to a method for making photoactive polymeric iodonium salts from capped novolak resin. The photoactive polymeric iodonium salts can be combined with a copper compound, as a cocatalyst, to provide thermal curing agents for cationically polymerizable organic materials.
As shown by Crivello et al., U.S. Pat. No. 4,151,175, assigned to the same assignee as the present invention, and incorporated herein by reference, diarylhalonium salts can be made by initially forming a diaryl iodonium bisulfate and thereafter effecting a metathesis reaction with a counterion source.
Polymer bound iodonium salts have been described as shown by Yamada and Okawara, Die Macromol. Chemie., 152, 153 (1972) by effecting reaction between iodinated polystyrene, benzene and sulfuric acid, or polystyrene with phenyl iodoso acetate in sulfuric acid.
The present invention is based on my discovery that if the phenolic hydroxyl group of a novolak resin is capped with an organic radical, such as a methyl or phenyl radical, and the resulting capped novolak resin is iodonated with an aryliodoso organic sulfonic acid, a polydiaryl iodonium organic sulfonic acid is formed such as a poly(diaryliodoniumtosylate). This polymeric iodonium salt can be metathesized with a polyhalometalloid alkali metal, or alkaline earth metal salt, such as sodium hexafluoroantimonate, to produce a photoactive polymeric iodonium salt. The photoactive polymeric iodonium salt can be combined with an effective amount of a copper compound as defined hereinafter, to provide a cocatalyst, useful for the thermal curing of cationically polymerizable organic materials.